1. Field of the Invention
This invention relates to novel fluorine-containing compounds useful as lubricants for precision machines and precision parts which require high-precision lubrication, and, as other chemical agents such as surfactants, releasing agents, rust preventives, etc., a process for preparing such fluorine-containing compounds, lubricant compositions containing said fluorine-containing compounds, and the magnetic recording media such as magnetic tapes, magnetic discs, etc., containing said fluorine-containing compounds in a lubricant layer.
2. Description of Prior Art
With the progressive tendency toward miniaturization and higher precision of machines and parts, the type of lubrication at sliding sections is being converted from fluid lubrication into boundary lubrication. Especially in the electronic machines and parts such as VTR, magnetic discs, etc., high-precision lubrication is required for the sliding motion between the magnetic tape or disc and the magnetic head because of the employment of thin ferromagnetic metal films purposed for improving recording density. For instance, in the deposited tapes or hard discs, in order to attain a maximum output by minimizing spacing loss between the magnetic recording medium and the magnetic head while securing the required durability and practical reliability, the lubricant layer formed at the surface of the magnetic layer is allowed to have a thickness of only several tens of .ANG.. Hence, development of an organic compound with excellent lubricating performance as a material for forming said lubricant layer is now an important subject for study in the art.
As the lubricants for the thin metal film type magnetic recording media, many fluorocarbon type lubricants have been proposed in view of the fact that the lubricants having a fluorocarbon chain in the molecule have good compatibility with the thin metal films (see, for example, Japanese Patent Application Kokai (Laid-Open) Nos. 61-107527, 61-107528, 61-107529, 62-92225, 62-92226 and 62-92227). Proposals have also been made for lubricants for magnetic recording media prepared by using a compound comprising perfluoroalkylpolyether chains (see, for example, U.S. Pat. No. 3,778,308 and JPN Pat. Appln. Kokai No. 60-109028).
On the other hand, as a preparation having a similar molecular structure to the fluorine-containing compounds of this invention, there has been proposed a surfactant having the following molecular structure: ##STR1## wherein R.sub.4 is hydrogen atom or an aliphatic alkyl group having 1-12 carbon atoms; R.sub.5 is an aliphatic alkylene group having 1, 2 or 5 carbon atoms; and h is an integer of 0 to 8 (U.S. Pat. No. 3,798,265).
It is imperative that a lubricant for thin metal film type magnetic recording media adheres strongly to the surface of thin metal film or protective film and the surface of the magnetic head to form the lubricant coating layers on said surfaces and is easily sheared between the lubricant molecules at the contact area of said coating layers, namely at the sliding area between the magnetic recording medium and the magnetic head. The perfluoroalkylpolyethers which have been used as lubricants for the magnetic recording media have good intermolecular shearing characteristics since the molecule surface is almost entirely covered with fluorine atoms, but they are weak in adhesive force to the surface of the thin metal film or protective film and the surface of magnetic head because of the weak polarity of their molecules. In order to overcome this defect, it has been proposed to introduce various types of polar group to the molecular terminals of perfluoroalkylpolyethers. However, when the molecular weight of the perfluoroalkylpolyether is greater than 3,000, the effect of introduction of a polar group is insufficient, and when the molecular weight is reduced for enhancing the effect of the polar group, there results a decrease in the amount of the lubricant due to its own evaporation because of the reduced intermolecular action of the perfluoroalkylpolyether. Thus, the perfluoroalkylpolyethers and their terminal-modified version were poor in adhesiveness to the thin metal film or protective film surface and the magnetic head surface and in stability, so that the lubricants prepared by using said compounds, especially those for thin metal film type magnetic recording media had the problems over durability and reliability, especially over use quality or performance under a low-humidity environment where cohesion of magnetic metal tends to occur at the magnetic head surface.
On the other hand, the fluorocarbon type lubricants disclosed in the afore-mentioned prior references have been applied to the thin metal film type magnetic recording media because of their good compatibility with thin metal films, but they are unsatisfactory in durability under an environment of a low humidity below 10% RH.
Here, a review is given of the prior references disclosing the processes resembling the fluorine-containing compound preparation process of this invention or the processes for preparing the compounds resembling the fluorine-containing compounds provided according to the present invention.
A process for preparing the compounds resembling the fluorine-containing compounds of the present invention is proposed in Japanese Patent Application Kokai No. 64-26539. The process of this prior application comprises hydrogenating a mixture of an unsaturated secondary amino-alcohol and a saturated secondary amino-alcohol and subjecting the resulting product to an epoxylation or esterification reaction to obtain a polyfluorinated amino-alcohol or an ester thereof.
According to this process, it is impossible to obtain a single fluorinated compound; the product is a mixture of the three fluorinated compounds with different molecular structures. Also, to obtain the fluorinated compounds with high purity, it is necessary to conduct purification with a silica column or other means, which leads to an elevated production cost.